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6. Temporal bone
The temporal bone is situated on the sides and the base of the cranium and lateral to the temporal lobe of cerebrum. Consists of five parts: * squamous part * mastoid part * petrous part * tympanic part * styloid process (or part) SQUAMOUS: The squamous part of the temporal bone is a very thin bone and forms the anterosuperior aspect of the temporal bone. The outer convex surface provides attachment to the temporalis muscle and forms a boundary of the temporal fossa. A curved line, the supramastoid crest (or temporal line), runs posterosuperiorly across its posterior part and provides attachment to the temporalis fascia. The anterior aspect of the squamous temporal bone extends antero and laterally to form the zygomatic process. The superior surface of the zygomatic process provides attachment to the temporalis fascia, whereas the inferior surface gives attachment of the masseter muscle. The posterior root runs above the external auditory meatus and continues with the supramastoid crest. The anterior root is directed medially and ends in the rounded, cartilage-covered, articular eminence, which forms the anterior boundary of the mandibular fossa. Articulations * superior border articulates with the parietal bone by temporoparietal suture * anteriorly it articulates with the zygomatic bone through zygomatic process * anteroinferiorly it articulates with the greater wing of sphenoid bone MASTOID: Posterolateral component, which is normally pneumatised by the mastoid air cells and is perforated by the mastoid foramen. The mastoid part has an outer rough surface provides attachment to occipitalis and auricularis posterior muscles. It continues inferiorly as the mastoid process, which is a conical bony projection that provides attachment for a number of muscles: * sternocleidomastoid * splenius capitis * the posterior belly of the digastric muscle * longissimus capitis muscles On the medial aspect of the mastoid process is a deep groove, called the digastric fossa, where the digastric muscles attach. Medial to this is the occipital groove, which is traversed by the occipital artery (off ECA). The sigmoid sulcus, which lodges part of the transverse sinus, lies in the inner surface of the mastoid portion. Articulations * the superior borders articulates with the mastoid angle of the parietal bone * the posterior border articulates with the inferior border of the occipital bone * anteriorly it is fused with the descending process of the squamous temporal bone PETROUS The petrous part of the temporal bone forms the part of skull base between the sphenoid and occipital bones. It houses the middle ear and inner ear components. The petrous temporal bone (PTB) has a pyramidal shape with an apex and a base as well as three surfaces and angles: * apex ** direct medially; articulates with posterior aspect of the greater wing of sphenoid and basilar occiput ** forms internal border of the carotid canal and the posterolateral boundary of the foramen lacerum * base ** directed laterally and fuses with the internal surface of squama temporalis and mastoid Surface * The anterior surface forms the posterior part of the middle cranial fossa. It is continuous with the inner surface of the squamous part united by the petrosquamous suture. ** Arcuate eminence at the center represent the location of the superior semicircular canal. ** Lateral to the arcuate eminence is a depression where the middle ear cavity lie. ** A shallow groove directed posterolaterally to open into the hiatus of the facial canal. ** Lateral to this hiatus a smaller opening for the lesser petrosal nerve. At the apex the termination of carotid canal is present. * The posterior surface forms the anterior part of posterior cranial fossa. It fuses with the inner surface of mastoid. ** internal acoustic meatus at its center ** posteriorly to the internal acoustic meatus is a small slit, leading to the canal of the vestibular aqueduct. * The inferior surface forms part of the exterior of the base of the skull. There are a number of foramina including: ** the inferior opening of the carotid canal ** the jugular foramen ** inferior tympanic canaliculus, through which the tympanic branch of the glossopharyngeal nerve passes. ** The stylomastoid foramen. It provides attachment to the levator veli palatini and the cartilaginous portion of the auditory tube. Angle * superior angle: attachment of tentorium cerebelli, its medial arm lodges the trigeminal nerve and the superior petrosal sinus lodges in the groove of the angle * posterior angle: contains a sulcus that lodges the inferior petrosal sinus medially and jugular notch of occipital bone forms the jugular foramen laterally * anterior angle: medial half articulates with the spinous process of the sphenoid and lateral half fuses with the squamous part by the petrosquamous suture TYMPANIC The tympanic part of the temporal bone is situated inferiorly to the squamous part and anteriorly to the mastoid part. It surrounds the external auditory meatus, forming the anterior wall, floor and some posterior wall of the bony external acoustic meatus. Laterally is the cartilaginous part of the external acoustic meatus and medially is the tympanic membrane. Its anteroinferior surface forms the posterior boundary of the mandibular fossa. It fuses medially with the petrous part and posteriorly with the squamous and mastoid part. STYLOID The styloid process is a slender pointed part of temporal bone. It projects inferiorly and anteriorly from the inferior surface of the temporal bone, and serves as an anchor point for several muscles associated with the tongue and larynx. * styloglossus muscle * stylohyoid muscle * stylopharyngeus muscle * stylohyoid ligament * stylomandibular ligament It should be noted all of these structures, along with the styloid process, develop from the second branchial arch and form the styloid apparatus. Muscles of T-bone * Tensor tympani muscle ** Dampens sound; hyperacusis if injured ** Innervation: V3 branch ** Location: Anteromedial wall, mesotympanum ** Attachment: Tendon inserts on malleus * Stapedius muscle ** Dampens sound; hyperacusis if injured ** Innervation: CN7 ** Location: Muscle belly in pyramidal eminence ** Attachment: Tendon attaches on head of stapes